The phrase gets used for two different things and both are correct in their own place. In fund economics it names the reason a young fund's multiples look weak: paid-in capital is large early while distributions and conservatively held marks are still small, so the ratio prints low almost by construction. That usage belongs to the private-markets fund-economics work and is not what follows.
What is the denominator effect in allocation?
In allocation the denominator effect is a mechanical consequence of marking one side of a portfolio faster than the other. Listed markets fall today. Private marks fall later, less, and by an amount an appraiser or a valuation committee decides. The private weight is a ratio whose numerator barely moves and whose denominator collapses, so the weight rises without anybody buying anything.
No transaction took place. The ratio moved on its own.
Put numbers on it. A portfolio of ₹800 crore public and ₹200 crore private sits at a 20.00% private weight. Assume private marks move 30% as far as public marks in the same period:
| Public fall | Private mark | Private weight | Overshoot above 20% | Private to sell to restore 20% |
|---|---|---|---|---|
| 20% | -6.0% | 22.71% | 2.71 pp | ₹22.40 crore |
| 30% | -9.0% | 24.53% | 4.53 pp | ₹33.60 crore |
| 40% | -12.0% | 26.83% | 6.83 pp | ₹44.80 crore |
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How do you rebalance, and what follows?
Check the rebalance at the 30% case: selling ₹33.60 crore of private and buying the same amount of public leaves ₹148.40 crore private against ₹593.60 crore public on an unchanged ₹742.00 crore total, which is exactly 20.00%.
Three things follow, and the third is the one that gets missed. A policy band written as a hard limit will force a sale at the worst possible price, so bands on illiquid sleeves should be soft, with a stated cure period measured in quarters rather than days. The overshoot is also partly an artefact and partly real, and separating them takes the unsmoothing correction: a sleeve whose marks lag is genuinely riskier than its reported weight suggests, so some of the overshoot is information rather than noise.
The third consequence is the expensive one. The effect runs in reverse when markets recover, and an investor who sold private assets at a discount into the fall then finds themselves under-weight into the rally, having paid the discount for the privilege.